In 1850 the German physicist Clausius formulated a proposition which has become known as the second law of thermodynamics. According to this well known theory, heat cannot of itself pass from a lower to a higher temperature, nor can it transform itself into useful work. The theory implies a negation by exclusion, namely that perpetual motion of the second order is not possible.
It is now known and accepted that entropy-reducing processes -- i.e. perpetual motion processes -- exist not only in imaginary experiments but also in reality. According to Clausius' theory, however, such a process must, by nature, always be combined with or join an entropy-increasing, destructive process which, according to his theory, must dominate and so undo that which the former process would achieve.